Continuous casting mold



2 Sheets-Sheet 1 Filed Oct. 20, 1964 INVENTOR. Temple W. RafcliffeATTORNEY 1967 I T, w. RATCLIFF'E 3,336,973

CONTINUOUS CASTING MOLD Filed Oct. 29, 1964 2 Sheets-Sheet 2 FIG.4

United States Patent 3,336,973 CONTINUOUS CASTING MDLD Temple W.Ratcliife, Beaver, Pa., assignor to The Babcock & Wilcox Company, NewYork, N.Y., a corporation of New York Filed Oct. 20, 1964, Ser. No.405,195 5 Claims. (Cl. 164-283) The present invention relates to thecontinuous casting of metals and more particularly to an improvedconstruction of fluid cooled molds utilized in the casting of highmelting temperature metals.

In the continuous casting of metals an upright open ended fluid cooledmold is arranged to receive a stream of molten metal at its upper endwithin an embryo casting withdrawn from its lower end. In solidifying ashell of solid metal on the casting, the heat of solidification, i.e.the heat that must be abstracted from the metal being cast to initiateand continue solidification, must be trans mitted to a cooling fluidpassing through flow passageways formed in the mold walls. In the usualcontinuous casting unit the cooling fluid consists of water which ispassed through the flow passageways in sufiicient quantity to obtain thenecessary cooling rate. Thus in the operation of continuous castingmolds there will be a temperature difference between the hot face of themold wall and the relatively cool face of the wall adjacent the coolingfluid flow passageways. While the mold wall temperature difference willbe substantially the same at any selected level in the mold, i.e. in aplane normal to the axis of the mold cavity, the hot face temperature ofthe mold will be different at diiferent points axially spaced along themold cavity from a maximum value adjacent the zone of the molten metallevel in the mold.

In the usual continuous casting unit the cooling water I is passedthrough the mold cooling fluid flow passageways in suflicient quantityto maintain a water leaving temperature of the order of 7 to F. abovethe entering water temperature. When casting steel, for example, the hotface of the mold in the zone of maximum temperature will be of the orderof 500 to 600 F. :above the cooling water temperatures.

Most continuous casting molds for large squares and slabs areconstructed of three general types. One of the types has involved theformation of the desired mold cross-sectional cavity by machining in asolid block of metal, such as copper. In this type of mold the coolingfluid flow passageways have been drilled through the block parallel toand spaced from the inner hot face of the mold. The location and numberof these drilled molds, relative to the mold hot face, is predicated onthe thermal properties of the metal from which the mold is made.

Another type of mold is constructed of heavy copper blocks with thecooling fluid flow passageways drilled therein, as in the solid blocktype, with several of the copper blocks assembled in a restrainingcontainer to define the mold cavity.

The third type of mold construction has utilized relatively thin platesor liners of metals having high thermal conductivity, such as copper orbrass, or the like, where the plates or liners are backed up by andsupported from massive steel members. In this type of mold the coolingfluid flow passageways are usually formed longitudinally of the moldwith intermediate supporting fins projecting inwardly from the containerand attached to the liners. Several of such plate assemblies areassembled to define the mold cavity. In all types of mold constructionthe temperature difference transversely of the mold wall andlongitudinally of the mold causes expansion difficulties which limit thelife of the mold. In the known block type of mold, the difliculties takethe form of stressing the hot face of the mold beyond its strengthlimits so that the mold must be periodically removed from operation andremachined to remove the fatigue cracks from the confining wall of themold cavity. Such difficulties are caused by the tendency of the hotface of the mold to expand in both lateral and longitudinal directionsto a greater extent than the cold face of the mold. The onepiececonstruction of the mold restrains lateral movement in particular, thusstressing the hot face of the metal beyond its elastic limit in at leastthe highest temperature zone of the mold. In the other types of mold thesame effects may be found provided the lateral ends or the intermediatefins of the walls are restrained by the container supporting the moldwalls. In addition, difiiculties are encountered at the joints betweenthe abutting edges of the mold walls. It will be understood in thisconnection that the lateral expansion of each mold wall will be greatestin the hot zone of the mold. If the corners of the mold walls are fullyrestrained the metal of the mold wall will attempt to form a convexconfiguration stressing the mold so as to reach a stress value leadingto premature termination of the casting operations. If the cornerrestraining forces are such as to permit expansion in the hot zone a gapwill be formed in the corners both above and below the hot zone of themold wall. In such circumstances any gap in the joints tends to befilled with the metal being cast, which can lead to a failure in thecontinuous casting operation by freezing in the mold gaps or by furtherdeformation of the mold wall due to the metal frozen in the gaps.

In the present invention, I provide a plurality of slots machinedinwardly from and extending the full length of the hot face of the moldand to a desired depth having at least sufficient lateral dimension tocompensate for thermal expansion of the mold hot faces. Each of theslots machined in the hot face of the mold is preferably filled with ametallic material having greater ductility than the face material of themold which permits thermal expansion of the material between the slotswithout overstressing the material therebetween. Advantageously, theinserts have been formed from the noble metals, such as gold, silver, orplatinum or alloys of these metals. One of the most desirable materialsfor use in the inserts is fine or high purity silver which issufliciently ductile to meet the requirements of the service indicated,has a high thermal conductivity, and is easily fused to the mold wallmetal. The characteristics of the silver include an exceptionally highthermal conductivity and a tendency to anneal itself at roomtemperatures after use at the high temperatures prevailing in anoperating continuous casting mold.

Alternatively, the walls in the segmented mold type of construction maybe formed with silver inserts or leaves, for example, extending throughthe mold wall so as to form a sandwich type of wall structure. Suchwalls may be formed by rolling or forging. As a further alternative,depending at least in part on the mold wall dimensions, the ductilemetal inserts or leaves may be located only or additionally at thecorners of the mold assembly.

The various features of novelty which characterize the invention arepointed out with particularity in the claims annexed to and forming apart oft his specification. For a better understanding of the invention,its operating advantages and specific objects attained by its use,reference should be had to the accompanying drawings and descriptivematter in which there is illustrated and described a preferredembodiment of the invention.

FIG. 1 is an elevation, in cross-section, of a continuous casting mold;

FIG. 2 is a horizontal plan view of the mold shown 'in FIG. 1;

FIG. 3 is an enlarged vertical view of a portion of the interior surfaceof a mold wall of the type shown in FIG. 2;

FIG. 4 is a further enlarged cross-section of a segment of the moldshown in FIG. 3 taken on the line 4-4; and

FIG. 5 is an alternative form of mold construction to that shown in FIG.4.

In the illustrated embodiment of the invention, the mold is usable in acontinuous casting unit such as shown in U.S. Patent No. 2,590,311. Theparticular mold shown is formed from a block of metal, such as copper,where,

the mold cavity is machined in the block with the crosssectionalconfiguration desired. As shown, the crosssection of the cavity isgenerally rectangular with bevelled corners Where the length of the moldcavity is greater than that of the width.

It will be appreciated that in accordance with the principles of thepresent invention, the mold could be constructed in the manner disclosedand claimed in US. Patent No. 2,867,018, where the confining walls ofthe mold are formedfrom relatively thin plates of copper or brass,backed by a massive steel casting. Either form of mold construction,i.e., a so-called block type or the plate type, is equally applicable tothe use of the present invention.

Referring to FIGS. 1 and 2, a block type mold having a rectangularcavity 12, is provided with a plurality of substantially equally spacedfluid flow passageways 11 extending throughout the length of the mold,with each passageway substantially uniformly spaced from the hot face 13of the mold wall.

In such a construction, the mold may be positioned with its axisvertical and when casting steel the hot face 13 of the mold will becontacted by molten metal at a temperature of the order of 2700 fluidpassing through the passageways 11 may be of the order of 50 F. Thetemperature gradient between the hot inner surface or face 13 which maybe at a temperature of 500 F. and the cooling fiow passageways 11 willfollow the usual temperature gradient characteristics, with the hotterportions of the mold walls being subjected to higher thermal expansionstresses than the relatively cooler portions. It will also be understoodthe temperature gradation longitudinally of the mold will vary from amaximum in the zone of initial molten metal contact with the mold wallsto a minimum adjacent the lower casting discharge end of the mold. Thereduction in the rate of heat transfer in the lower zone is due toshrinkage of the casting from the mold walls with the imposition of aninsulating gap between the casting and the confining mold surface.

As shown in FIG. 3, the length of the mold may, for convenience, bedivided into a plurality of zones which are exposed to different ratesof heat transfer. The uppermost zone A extends downwardly from the upperedge of the mold cavity to a position approximately that of, orimmediately above, the upper level of the molten metal pool maintainedin the mold. Since the molten metal is usually poured into the upper endof the mold cavity, the Walls in this zone will obtain heat by radiationupwardly from the meniscus of the molten metal pool and from theincoming stream of metal.

It will be appreciated the level of the molten metal in the mold cavityis not usually fixed and will vary somewhat even when the operatorintends to maintain such level at a constant value. The great majorityof continuous casting units deliberately vary the molten metal in themold either by cyclic reciprocation of the mold itself or by variationin the rate of casting withdrawal from the mold. Also, an exactcoordination of the pour rate with the casting withdrawal is improbablewhen casting steel due to the erosive and corrosive character of moltensteel in contact with the refractories defining the metal flow path tothe mold. Thus the lower limit of zone A, and the upper limit of theadjoining zone B, cannot be exactly at the level of the molten metalpool in the mold cavity.

F., while the cooling in this area and may reheat and expand toreestablish contact with the wall of the mold. The lowermost zone D willhave a relatively low heat exchange rate between the wall and thecasting due to the normal formation and maintenance of an air gapbetween the casting and the wall of the mold.

In accordance with the invention, the hot face of the mold wall isslotted to a desired depth dependent upon the type and design of moldutilized. The width of the slot need only be enough to permitsubstantially unrestrained expansion of each preselected unit in apattern. For example, if the slots are made on one inch centers, theyshould be wide enough to allow free linear expansion of the interveninginch of mold metal up to its operating temperature. Assuming the hotface of the mold to be 500 F. to 600 F. above the water cooled face ofthe mold, the slot width for copper or -15 brass would be of the orderof four to five thousandths of an inch (.004 to .005). The machining ofa slot of this width is difficult, if not impossible, and I select aslot width that is machinable, such as ten to twenty thousandths of aninch and fill the slot with a ductile strip or filler so that expansionof the mold wall can occur, and the metal being cast will not key in theslots and disrupt casting operations.

In the portion of the mold 10 shown in FIGS. 3 and 4, slots 21 aremachined in the inner surface of the mold wall and extend from the upperedge 20 to the lower edge 22 of the mold. The slots 21 are parallel toeach other and to the longitudinal axis of the mold. In the embodimentshown the slots 21 are two inches apart with shorter slots 23 machinedin parallel with and between the slots 21, in the zones B and C only.Similar slots 24 are machined in the mold wall transversely of the moldaxis and throughout the periphery of the mold. In the zone D the slots24 may be further apart than in the other zones, being closer in zone Bthan in either zone A or C. The spacing of the slots is dependent uponthe amount of thermal expansion expected in the mold wall in dilferentzones.

As shown particularly in FIG. 4, the slots 21 and 23 are machinedapproximately one-half the depth of the wall between the hot face 13 andthe adjoining surface of the fiuid fiow passageway 11. In the exampleshown, the depth of each of the slots is approximately 7 All of theslots are approximately of the same depth and width. Preferably theslots are filled with fine silver to form the inserts 25 where theinserts are brazed or otherwise attached to the metal of the mold wallfor good thermal contact therebetween.

In the described construction, the thermal distortion of mold walls issubstantially reduced particularly in the region of highesttemperatures. In addition, the temperature changes and mold flexing atthe bottom of the slots occur where the temperature differences are oflesser values relative to the hot surface of the wall and where thematerials have better fatigue properties, thereby resulting in adecidedly improved mold service life.

In operation, as the mold wall is heated, differential thermal expansionoccurs and the inserts 25, being more ductile than the material of thewall, will be compressed without overstressing the material of the Wall.During compression of the inserts 25, some of the metal thereof Will bedisplaced beyond the surface 13 of the mold, but the displacement willbe minor and will not ordinarily interfere with the casting operations.However, under some unusual circumstances it may be desirable to indentthe surface of the insert as shown in FIG. 5. In such circumstances thesurface 26 of the insert will be grooved or cut to form an inwardlycurved surface when the mold is at ambient temperatures so that atoperating temperatures the surface of the insert will be substantiallyflush with the surface 13 of the mold. The maximum depth of the curvedsurface 26, when cold, need be only a few' thousandths of an inch.

While in accordance with the provisions of the statutes there isillustrated and described herein a specific embodiment of the invention,those skilled in the art will understand that changes may be made in theform of the invention covered by the claims, and that certain fea turesof the invention may sometimes be used to advantage without acorresponding use of the other features.

What is claimed is:

1. A continuous casting mold comprising walls defining an open endedcavity to receive molten metal delivered to one end and to discharge anembryo casting from the opposite end thereof, means defining coolingfluid flow passageways to cool the walls of said mold, means formingslots extending outwardly from the interior surfaces of said mold cavitypartially through the mold walls to relieve thermal operational stressesin the said mold walls, and metal inserts of greater ductility than theface material of the mold positioned in said slots, said inserts beingsubstantially flush with the inner surface of said mold Walls when atoperational temperature.

2. A continuous casting mold according to claim 1 wherein said insertsare formed of high purity silver.

3. A continuous casting mold according to claim 1 wherein said ductilemetal inserts are installed with a curved surface adjacent the innersurface of said mold wall.

4. A continuous casting mold according to claim 1 wherein some of saidductile metal strips extend parallel to the axis of said mold cavitythroughout the length of said mold and some of said strips extend normalto the axis of and around the periphery of said mold cavity.

5. A continuous casting mold according to claim 1 wherein said insertsare formed of metal selected from the group consisting of gold,platinum, silver and their alloys.

References Cited UNITED STATES PATENTS 481,442 8/1892 Treat 22177528,034 10/1894 Schon 22-177 532,888 1/1895 Matheus 22-177 1,634,9997/1927 Krause 24979 2,479,191 8/1949 Williams et a1. 22l77 2,683,332 7/1954 Litalien et al 22-177 XR 3,203,055 8/ 1965 Bungeroth et al 22-57.2

J. SPENCER OVERHOLSER, Primary Examiner. R. S. ANNEAR, AssistantExaminer.

1. A CONTINUOUS CASTING MOLD COMPRISING WALLS DEFINING AN OPEN ENDEDCAVITY TO RECEIVE MOLTEN METAL DELIVERED TO ONE END AND TO DISCHARGE ANEMBRYO CASTING FROM THE OPPOSITE END THEREOF, MEANS DEFINING COOLINGFLUID FLOW PASSAGEWAYS TO COOL THE WALLS OF SAID MOLD, MEANS FORMINGSLOTS EXTENDING OUTWARDLY FORM THE INTERIOR SURFACES OF SAID MOLD CAVITYPARTIALLY THROUGH THE MOLD WALLS TO RELIEVE THERMAL OPERATIONAL STRESSESIN THE SAID MOLD WALLS, AND METAL INSERTS OF GREATER DUCTILITY THAN THEFACE MATERIAL OF THE MOLD POSITIONED IN SAID SLOTS, SAID INSERTS BEINGSUBSTANTIALLY FLUSH WITH THE INNER SURFACE OF SAID MOLD WALLS WHEN ATOPERATIONAL TEMPERATURE.